Hi,

  To what has already been said I think the two round-robin articles are a 
must-read about this issue, as they compare refinement of neutron and X-ray 
data for a given (simple) compound. They are a bit old, especially by today's 
synchrotron standards, but are still very interesting :

1) J. Appl. Cryst. (1992). 25, 589-610 "Rietveld refinement round robin. I. 
Analysis of standard X-ray and neutron data for PbSO4"

  => http://dx.doi.org/10.1107/S0021889892003649

2) J. Appl. Cryst. (1994). 27, 802-844 "Rietveld refinement round robin. II. 
Analysis of monoclinic ZrO2"

  => http://dx.doi.org/10.1107/S0021889894000646

  Jump to figure 6 of the first article if you haven't read them already and 
are in a hurry.

  Of course these articles are both worst-case scenari for the X-rays, as you 
want accurate oxygen positions beside one heavy (Pb or Zr) atom.

  It's also always interesting to point out the distribution curve on the 
_isotropic_ displacement parameters (article 1 fig 7) when you are tempted to  
to use anistropic ones.

        Vincent
-- 
Vincent Favre-Nicolin
Université Joseph Fourier
ObjCryst & Fox : http://objcryst.sourceforge.net

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